1. Field of the Invention
This invention relates to a digital television signal receiving unit (hereinafter merely called a receiving unit) that is preferable for receiving a digital type television signal transmitted by a ground wave.
2. Description of the Related Art
FIG. 4 illustrates a block arrangement of a related art receiving unit, wherein the receiving unit consists of a tuner section 31, an OFDM demodulation circuit section 32, a Fourier transform circuit section 33, an error correction circuit section 34, a control circuit section 35, a connector 36 having a plurality of contact elements and a crystal oscillator 37 and the like are mounted on a printed circuit board 41.
In this case, the tuner section 31 has a rectangular parallelpiped metallic case 31a and it is constructed such that a frequency conversion circuit and an A/D conversion circuit and the like (both of them are not shown) are mounted on a printed circuit board (not shown) housed in the metallic case 31a. Then, an input connector 31b receiving the television signal is fixed at the side surface under a state in which it is protruded in a longitudinal direction of the metallic case 31a and further the metallic case 31a has a plurality of terminals 31c protruded from the other side surface.
In this case, the OFDM demodulation circuit section 32, the Fourier transform circuit section 33, the error correction circuit 34 and the control circuit section 35 is formed into one integrated circuit chip and each of them is constructed as its individual package.
The printed circuit board 41 consists of by a rectangular multilayer substrate. The tuner section 31 is mounted on the printed circuit board 41 in such a way that the input connector 31b is protruded out of the end section 41a of the printed circuit board 41. A plurality of terminals 31c protruded out of the side surface of the tuner section 31 are bent at a right angle and inserted into the printed circuit board 41. In addition, the OFDM demodulation circuit section 32 and the Fourier transform circuit section 33 are arranged in sequence on the same lines arranged in the longitudinal direction of the tuner section 31, the tuner section 31 and the OFDM demodulation circuit section 32 are mounted in such that they are near to each other and the OFDM demodulation circuit section 32 and the Fourier transform circuit section 33 are also mounted in such that they are near to each other.
The error correction circuit section 34 oppositely faces against the OFDM demodulation circuit section 32, the control circuit section 35 faces oppositely against the Fourier transform circuit 33 and are mounted such that they are positioned in parallel near the arrangement of the OFDM demodulation circuit section 32 and the Fourier transform circuit section 33. Then, a crystal oscillator 37 is mounted between the error correction circuit section 34 and the control circuit section 35.
Further, the connector 36, having a plurality of connecting elements, is mounted in opposition to the terminals 31c of the tuner section 31.
Then, the terminals 31c of the tuner section 31 and each of the terminals (not shown) of the OFDM demodulation circuit section 32, the Fourier transform circuit section 33, the error correction circuit section 34 and the control circuit 35 and the like is soldered to a predetermined conductive pattern (not shown) arranged on the printed circuit board 41 and connected to each other and connected to the contact elements (not shown) of the connector 36. Then, various kinds of signals are generated by or received from the main body of the television receiver set through the connector 36.
The tuner section 31 includes the frequency conversion circuit and the A/D conversion circuit, wherein a television signal of a tuned channel is converted into an intermediate frequency signal by the frequency conversion circuit, and the A/D conversion circuit may output a digital signal generated by sampling the intermediate frequency signal to the OFDM demodulation circuit section 32.
In this arrangement, the printed circuit board 41 is provided with a conductive pattern (not shown), the terminals 31c of the tuner section 31 are connected to the OFDM demodulation circuit section 32 through this conductive pattern, the OFDM circuit section 32 and the Fourier transform circuit section 33 are connected to each other, and the OFDM demodulation circuit section 32 and the error correction circuit section 34 are connected to each other to transmit the aforesaid signal in sequence.
The control circuit section 35 is a microcomputer, wherein it controls operations of the OFDM demodulation circuit section 32, the Fourier transform circuit section 33 and the error correction circuit section 34 in response to a control signal (that includes a tuning signal) sent from the main body of the television receiver (not shown) and further controls a tuning operation of the tuner section 31.
Due to this fact, the control circuit section 35 and the terminals 31c; the control circuit section 35 and the OFDM demodulation circuit 32; the control circuit section 35 and the error correction circuit section 34; and the control circuit section 35 and the Fourier transform circuit section 33 are connected to each other to generate or receive the aforesaid control signal.
Further, the crystal oscillator 37 is used for generating a synchronous signal in case where the control circuit section 35 controls the operations of the OFDM demodulation circuit section 32 and the error correction circuit section 34.
In the aforesaid receiving unit, since the tuner section 31 and the crystal oscillator 37 were fixed on the printed circuit board 41, its assembling work became a troublesome work and at the same time its cost was increased under application of either the printed circuit board 41 or the connector 36.
In addition, since the OFDM demodulation circuit section 32 to the error correction circuit section 34 were not shielded and mounted on the printed circuit board 41, noises such as synchronizing signals (a vertical synchronizing signal and a horizontal synchronizing signal and the like) outputted from the main body part of the television receiver were induced at each of these circuit sections to be overlapped on the MPEG bit stream signal. This caused the image quality or the like to deteriorate. In cases where a level of the synchronizing signal is further high, this state produces some problems that badly influences the operations of the OFDM demodulation circuit section 32 or the error correction circuit section 34 and a reproduction of the accurate image becomes impossible.
In view of the foregoing, the present invention decreases costs by simplifying receiver structure and minimizing units influence to noise generated by the main body of the television receiver.
A digital television signal receiving unit embodiment of the present invention comprises a metallic case, a frequency conversion circuit for converting a frequency of a received digital television signal into an intermediate frequency signal or a base band signal and an OFDM signal processing circuit for processing either the intermediate frequency signal or the base signal and outputting an MPEG bit stream signal, housed in the metallic case. Operations of the frequency conversion circuit and the signal processing circuit are controlled by a control signal outputted from a control circuit arranged outside the metallic case.
In addition, a digital television signal receiving unit embodiment according to the present invention includes an OFDM signal processing circuit comprised of an A/D conversion circuit for converting either the intermediate frequency signal or the base band signal into a digital signal and an OFMD demodulation circuit for OFDM demodulating the digital signal and outputting a demodulation signal. This embodiment further includes a Fourier transform circuit for Fourier-transforming the demodulation signal and an error correction circuit for correcting a bit error of the signal Fourier-transformed by the Fourier transform circuit and outputting the MPEG bit stream signal. Preferably, the OFDM demodulation circuit, the Fourier transform circuit and the error correction circuit are packaged or integrated within one integrated circuit chip. In addition, a digital television signal receiving unit embodiment of the present invention includes an A/D conversion circuit formed within the integrated circuit chip.
In addition, a digital television signal receiving unit embodiment according to the present invention includes a printed circuit board housed in the metallic case, the frequency conversion circuit and the integrated circuit are mounted on the printed circuit board, terminals for receiving the control signal and inputting it into the integrated circuit through a wiring conductive pattern arranged on the printed circuit board are fixed to one side surface of the metallic case, and the terminals are positioned between the mounting position of the frequency conversion circuit and the mounting position of the integrated circuit.